The invention relates generally to head positioning servo systems for reducing misalignment between heads and data tracks in data storage systems.
In multi-track magnetic tape storage systems, random lateral tape motion (“LTM”) is a limiting factor in achieving higher track densities and higher user data capacity per tape. LTM is the random motion of a tape in a direction lateral to the direction of tape transport. LTM is impacted by variations in tension, number of tape guides used, as well as other factors. These factors affect LTM in various ways. Some may cause abrupt momentary jumps while others may cause a gradual shift over time. During a read, LTM causes mis-registration of the read head over the track being read. Such mis-registration results in read data error.
Various servo techniques or approaches have been developed to reduce the effects of tracking error caused by LTM and thus improve track density. Although known servo techniques vary somewhat, most involve mechanisms for dynamically moving the read head laterally to continually re-position it over the recorded data track. They also use servo heads to provide corrective positioning information. For example, one approach reads recorded servo information, either dedicated (that is, located on a continuous track of servo information) or embedded within the user data, to produce a position error signal for accurate head positioning. Yet another approach uses two auxiliary servo heads to follow each edge of an adjacent data track to produce a position error signal. In both of these approaches, the position error signal is based on signal amplitude.